A variety of injection molded parts are made and used for automobile body and trim parts. For example, bumpers, spoilers, body panels, doors, filler panels, wheel covers, dashboards, arm rests and other parts are commonly made by the injection molding of thermoplastic materials.
In order to provide a painted or other decorative surface for injection molded plastic trim parts, film lamination techniques are commonly employed. A paint film laminate is insert molded or, as it is sometimes referred to, co-molded, with the desired thermoplastic to fuse the film over the injection molded substrate. The resulting injection molded film-plastic part is ready for assembly without subsequent painting.
The paint film laminate used in these insert molding techniques may comprise a backing sheet to which paint, other pigment-containing, or clear layers are adhered. Typically, the backing sheet comprises an extruded thermoplastic sheet. The paint or pigment layer may contain colored pigments or reflective flake pigments such as aluminum or mica flakes to provide for example a metallic finish.
The paint film may consist of a monocoat; a clear coat over a base coat; or a clear coat and a base coat with interposed print or design. The paint film, including base coat, clear coat and print or design, if desired, may range from about 0.5-4 mil. (13-100 .mu.m) in thickness.
Laminated paint films are well known in the art and are available, for example, from Avery Dennison Decorative Films Div. of Schererville, Ind., or Rexham Decorative Products of Charlotte, N.C. For example, laminated paint films are described in U.S. Pat. No. 5,514,427, the disclosure of which is incorporated herein by reference. The films are typically provided in a roll, unwound and then "preformed" to a size and shape approximating that of the final injection molded film-plastic part.
The paint film laminate preform is next usually trimmed and placed along the cavity side of an injection mold with the painted side or "show" side thereof facing the mold cavity surface. Trimming may be accomplished by hand or in some instances by the use of heavy stamping machines that require the use of expensive tooling.
After trimming, the paint film laminate preform is ready for the molding process where it may be placed along the core side of the mold. The mold is then clamped and the desired molten resin is injected into the mold cavity. Heat and pressure conditions in the mold partially melt the backing sheet and a melt bonding or fusion of the injected resin and the backing sheet of the film occur. Injection molds used for these processes are rear or edge gated so that the molten resin is directed along the backside of the film.
Techniques for preforming paint film laminates and insert molding film-plastic parts are disclosed in U.S. Pat. Nos. 5.599,608; 5,759,477; and 5,783.287. The disclosure of these patents is incorporated herein by reference.
While the prior art process described above has proven effective in many respects, there is a need in the art to improve upon the trimming step for the paint film laminate so that this operation can be conducted economically and more accurately. At the same time, it is desirable to minimize the use of heavy stamping or cutting machines that require large spatial areas and expensive cutting tools and dies.
It is even more desirable to provide a laser trimming operation wherein operation of the laser is conducted in an enclosed atmosphere, shielding workers from the laser beam and from soot and vapors that emanate from the cutting operation. Another desirable goal is to provide an automated laser trimming apparatus wherein soot and vapors from the laser cutting area are immediately removed from the trimming area to a bag house or other filter mechanism and wherein the trimmed workpiece does not contain burned or charred areas surrounding the laser trimming line.